1. Field of the Invention
The present invention relates to a vane for a centrifugal throwing wheel and, more particularly, to a vane for a centrifugal throwing wheel which exhibits improved shot distribution and wear characteristics.
2. Description of the Related Art
Centrifugal throwing wheels and vanes (blades) associated with them can be used to propel abrasive at high speed onto a work surface that is to be abraded, prepared or otherwise surface treated. Typically, a number of blades are radially attached to the throwing wheel and are configured such that abrasive material can be fed onto the heel of the blade and then accelerated along the length of the blade by the angular velocity of the wheel. The abrasive material leaves the outermost end of the vane and contacts the work surface. Depending on the specific application, a wide variety of abrasives may be used including steel shot, steel grit, wire, and crushed shells.
Often, it may be desirable to control the shot pattern that is obtained with a blasting apparatus. For different applications, the optimum shot pattern may be either tight and concentrated or broad and dispersed. When one of the goals of the shot blasting procedure is to quickly and evenly abrade a work surface, it may be desirable for the shot to cover as broad an area as possible, but the shot pattern should also be consistent to reduce uneven abrasion. Several different types of blade designs have been used in an effort to achieve this goal. For example, a vane with slightly flaring, rather than straight, sidewalls is disclosed by Carpenter in U.S. Pat. No. 4,941,297. This feature allows any particles that happen to be directed laterally to spread out rather than be contained by the channel provided by a vane with essentially parallel edges. Another approach was disclosed by Fuerst in U.S. Pat. No. 3,436,867, which discloses a vane having a leading surface that is convex in the direction of wheel rotation and parallel side walls. This convex shape serves to accelerate the particles laterally.
Another persistent, art-recognized problem is the uneven wearing of throwing vanes. As shot is accelerated down the surface of a vane, it tends to take the shortest path to the tip, absent any forces other than that supplied by the angular velocity of the wheel. As a result, conventional vanes exhibit excessive wear along their centerline and, consequently, they must be replaced more often than would be required if the shot wore the vanes evenly across the entire leading surface. Alternatively, vanes such as those described by Fuerst that distribute abrasive laterally tend to wear most quickly along the side walls where the majority of abrasive is concentrated. As the cost of abrasive material and replacement vanes for centrifugal throwing wheels has continued to rise, the surface treatment industry has developed a long felt, yet unsolved need for a centrifugal throwing vane having improved shot distribution and wear characteristics.
Accordingly, the present invention is directed to a vane for a centrifugal throwing apparatus. The vane has a convex leading surface and flared edges to provide a consistent, broad blast pattern and improved wear characteristics.
In one embodiment, the vane includes a pickup end, a discharge end opposed to the pickup end, and a leading surface connecting the pickup end to the discharge end. A portion of the leading surface is convex in cross section. Two opposed longitudinal edges define the leading surface, with at least one of the edges being outwardly flared.
In various alternative embodiments, both of the two opposed longitudinal edges may be outwardly flared. The leading surface may be convex from a point on the leading surface where laminar flow begins. The radius of convexity may increase between the pickup end and the discharge end of the vane. At least one of the edges may be flared outwardly at an increasing rate from the start of the flare to the discharge end of the vane.
In another alternative embodiment, the vane includes a longitudinal raised rail formed near one edge of the leading surface, the rail being outwardly flared. A portion of the leading surface is convex in cross section. The radius of convexity may increase between the pickup end and the discharge end of the vane. Alternatively, the vane may include a raised rail on each side of the leading surface, both of the rails being outwardly flared. At least one of the rails may be flared outwardly at an increasing rate from the start of the flare to the discharge end of the vane.